Towards Small-Molecule CXCR3 Ligands with Clinical Potential

7D, a small molecule inhibits dengue infection by increasing interferons and neutralizing-antibodies via CXCL4:CXCR3:p38:IRF3 and Sirt1:STAT3 axes respectively

There are a limited number of effective vaccines against dengue virus (DENV) and significant efforts are being made to develop potent anti-virals. Previously, we described that platelet-chemokine CXCL4 negatively regulates interferon (IFN)-α/β synthesis and promotes DENV2 replication. An antagonist to CXCR3 (CXCL4 receptor) reversed it and inhibited viral replication. In a concurrent search, we identified CXCR3-antagonist from our compound library, namely 7D, which inhibited all serotypes of DENV in vitro. With a half-life of ~2.85 h in plasma and no significant toxicity, 7D supplementation (8 mg/kg-body-weight) to DENV2-infected IFNα/β/γR-/-AG129 or wild-type C57BL6 mice increased synthesis of IFN-α/β and IFN-λ, and rescued disease symptoms like thrombocytopenia, leukopenia and vascular-leakage, with improved survival. 7D, having the property to inhibit Sirt-1 deacetylase, promoted acetylation and phosphorylation of STAT3, which in-turn increased plasmablast proliferation, germinal-center maturation and synthesis of neutralizing-antibodies against DENV2 in mice. A STAT3-inhibitor successfully inhibited these effects of 7D. Together, these observations identify compound 7D as a stimulator of IFN-α/β/λ synthesis via CXCL4:CXCR3:p38:IRF3 signaling, and a booster for neutralizing-antibody generation by promoting STAT3-acetylation in plasmablasts, capable of protecting dengue infection.

Phosphatidylserine-incorporated exosome mimetics encapsulating CXCR3 antagonist alleviate osteoporosis

Exosomes derived from mesenchymal stem cells are an active area of research due to their therapeutic potential in treating osteoporosis. To further harness their therapeutic performance in modulating bone resorption, we have equipped exosomes with osteoclast-targeting moieties on their surface as well as chemokine receptor antagonists blocking osteoclast recruitment. Phosphatidylserine (PS), a membrane lipid exerting immunosuppressive and phagocytic signals, was incorporated in the membrane of exosome mimetics (EMs) to achieve a marked affinity for osteoclast precursors and potential anti-resorptive effects. We also aimed to tackle a CXCL9-CXCR3 ligand-receptor axis, a critical signaling axis in regulating osteoclast precursor recruitment and differentiation at bone resorption sites, by encapsulating a chemical antagonist of CXCR3, AMG487, in the PS-incorporated EMs (PS-EMs). The osteoclast-targeting PS-EMs loaded with AMG487 effectively protected against bone loss in an ovariectomized mouse model. Our findings demonstrate the great promise of PS-EMs as anti-resorptive nanotherapies for alleviating osteoporosis.

CXCR3 participates in asymmetric division of mouse oocytes by modulating actin dynamics

Extensive research has been conducted on the role of CXCR3 in immune responses and inflammation. However, the role of CXCR3 in the reproductive system, particularly in oocyte development, remains unknown. In this study, we present findings on the involvement of CXCR3 in the meiotic division process of mouse oocytes. We found CXCR3 was expressed consistently throughout the entire maturation process of mouse oocyte. Inhibition of CXCR3 impaired the asymmetric division of oocyte, while the injection of Cxcr3 mRNA was capable of restoring these defects. Further study showed that inhibition of CXCR3 perturbed spindle migration by affecting LIMK/cofilin pathway-mediated actin remodeling. Knockout of CXCR3 led to an upregulation of actin-binding protein and an increased ATP level in GV-stage oocytes, while maintaining normal actin dynamics during the process of meiosis. Additionally, we noticed the expression level of DYNLT1 is markedly elevated in CXCR3-null oocytes. DYNLT1 bound with the Arp2/3 complex, and knockdown of DYNLT1 in CXCR3-null oocytes impaired the organization of cytoplasmic actin, suggesting the regulatory role of DYNLT1 in actin organization, and the compensatory expression of DYNLT1 may contribute to maintain normal actin dynamics in CXCR3-knockout oocytes. In summary, our findings provide insights into the intricate network of actin dynamics associated with CXCR3 during oocyte meiosis.

A review of the pleiotropic actions of the IFN-inducible CXC chemokine receptor 3 ligands in the synovial microenvironment

Chemokines are pivotal players in instigation and perpetuation of synovitis through leukocytes egress from the blood circulation into the inflamed articulation. Multitudinous literature addressing the involvement of the dual-function interferon (IFN)-inducible chemokines CXCL9, CXCL10 and CXCL11 in diseases characterized by chronic inflammatory arthritis emphasizes the need for detangling their etiopathological relevance. Through interaction with their mutual receptor CXC chemokine receptor 3 (CXCR3), the chemokines CXCL9, CXCL10 and CXCL11 exert their hallmark function of coordinating directional trafficking of CD4+ TH1 cells, CD8+ T cells, NK cells and NKT cells towards inflammatory niches. Among other (patho)physiological processes including infection, cancer, and angiostasis, IFN-inducible CXCR3 ligands have been implicated in autoinflammatory and autoimmune diseases. This review presents a comprehensive overview of the abundant presence of IFN-induced CXCR3 ligands in bodily fluids of patients with inflammatory arthritis, the outcomes of their selective depletion in rodent models, and the attempts at developing candidate drugs targeting the CXCR3 chemokine system. We further propose that the involvement of the CXCR3 binding chemokines in synovitis and joint remodeling encompasses more than solely the directional ingress of CXCR3-expressing leukocytes. The pleotropic actions of the IFN-inducible CXCR3 ligands in the synovial niche reiteratively illustrate the extensive complexity of the CXCR3 chemokine network, which is based on the intercommunion of IFN-inducible CXCR3 ligands with distinct CXCR3 isoforms, enzymes, cytokines, and infiltrated and resident cells present in the inflamed joints.

Blockade of the CXCR3/CXCL10 axis ameliorates inflammation caused by immunoproteasome dysfunction

Immunoproteasomes regulate the degradation of ubiquitin-coupled proteins and generate peptides that are preferentially presented by MHC class I. Mutations in immunoproteasome subunits lead to immunoproteasome dysfunction, which causes proteasome-associated autoinflammatory syndromes (PRAAS) characterized by nodular erythema and partial lipodystrophy. It remains unclear, however, how immunoproteasome dysfunction leads to inflammatory symptoms. Here, we established mice harboring a mutation in Psmb8 (Psmb8-KI mice) and addressed this question. Psmb8-KI mice showed higher susceptibility to imiquimod-induced skin inflammation (IMS). Blockade of IL-6 or TNF-α partially suppressed IMS in both control and Psmb8-KI mice, but there was still more residual inflammation in the Psmb8-KI mice than in the control mice. DNA microarray analysis showed that treatment of J774 cells with proteasome inhibitors increased the expression of the Cxcl9 and Cxcl10 genes. Deficiency in Cxcr3, the gene encoding the receptor of CXCL9 and CXCL10, in control mice did not change IMS susceptibility, while deficiency in Cxcr3 in Psmb8-KI mice ameliorated IMS. Taken together, these findings demonstrate that this mutation in Psmb8 leads to hyperactivation of the CXCR3 pathway, which is responsible for the increased susceptibility of Psmb8-KI mice to IMS. These data suggest the CXCR3/CXCL10 axis as a new molecular target for treating PRAAS.

PET Imaging Radiotracers of Chemokine Receptors

Chemokines and chemokine receptors have been recognized as critical signal components that maintain the physiological functions of various cells, particularly the immune cells. The signals of chemokines/chemokine receptors guide various leukocytes to respond to inflammatory reactions and infectious agents. Many chemokine receptors play supportive roles in the differentiation, proliferation, angiogenesis, and metastasis of diverse tumor cells. In addition, the signaling functions of a few chemokine receptors are associated with cardiac, pulmonary, and brain disorders. Over the years, numerous promising molecules ranging from small molecules to short peptides and antibodies have been developed to study the role of chemokine receptors in healthy states and diseased states. These drug-like candidates are in turn exploited as radiolabeled probes for the imaging of chemokine receptors using noninvasive in vivo imaging, such as positron emission tomography (PET). Recent advances in the development of radiotracers for various chemokine receptors, particularly of CXCR4, CCR2, and CCR5, shed new light on chemokine-related cancer and cardiovascular research and the subsequent drug development. Here, we present the recent progress in PET radiotracer development for imaging of various chemokine receptors.

Cxcl9l and Cxcr3.2 regulate recruitment of osteoclast progenitors to bone matrix in a medaka osteoporosis model

Bone remodeling requires a balanced interplay of osteoblasts and osteoclasts. While the intercellular signaling that triggers bone cell differentiation is well understood, it remains unclear how bone progenitor cells are recruited to remodeling sites. Various chemokines are upregulated under osteoporotic conditions. However, whether they are involved in progenitor recruitment or instead have inflammatory roles is unknown. Here we used a medaka fish osteoporosis model to identify the chemokine ligand Cxcl9l and receptor Cxcr3.2 as essential to control osteoclast progenitor recruitment and differentiation at bone resorption sites. Cxcr3.2 activity can be blocked by small-molecule inhibitors that protect bone from osteoporotic insult. Our study demonstrates the potential of fish for osteoporosis drug discovery and opens avenues for future osteoporosis therapy.

Bone homeostasis requires continuous remodeling of bone matrix to maintain structural integrity. This involves extensive communication between bone-forming osteoblasts and bone-resorbing osteoclasts to orchestrate balanced progenitor cell recruitment and activation. Only a few mediators controlling progenitor activation are known to date and have been targeted for intervention of bone disorders such as osteoporosis. To identify druggable pathways, we generated a medaka (Oryzias latipes) osteoporosis model, where inducible expression of receptor-activator of nuclear factor kappa-Β ligand (Rankl) leads to ectopic formation of osteoclasts and excessive bone resorption, which can be assessed by live imaging. Here we show that upon Rankl induction, osteoblast progenitors up-regulate expression of the chemokine ligand Cxcl9l. Ectopic expression of Cxcl9l recruits mpeg1-positive macrophages to bone matrix and triggers their differentiation into osteoclasts. We also demonstrate that the chemokine receptor Cxcr3.2 is expressed in a distinct subset of macrophages in the aorta-gonad-mesonephros (AGM). Live imaging revealed that upon Rankl induction, Cxcr3.2-positive macrophages get activated, migrate to bone matrix, and differentiate into osteoclasts. Importantly, mutations in cxcr3.2 prevent macrophage recruitment and osteoclast differentiation. Furthermore, Cxcr3.2 inhibition by the chemical antagonists AMG487 and NBI-74330 also reduced osteoclast recruitment and protected bone integrity against osteoporotic insult. Our data identify a mechanism for progenitor recruitment to bone resorption sites and Cxcl9l and Cxcr3.2 as potential druggable regulators of bone homeostasis and osteoporosis.

Chemokine receptor CXCR3 is required for lethal brain pathology but not pathogen clearance during cryptococcal meningoencephalitis

Cryptococcal meningoencephalitis (CM) is the major cause of infection-related neurological death, typically seen in immunocompromised patients. However, T cell-driven inflammatory response has been increasingly implicated in lethal central nervous system (CNS) immunopathology in human patients and murine models. Here, we report marked up-regulation of the chemokine receptor CXCR3 axis in human patients and mice with CM. CXCR3 deletion in mice improves survival, diminishes neurological deficits, and limits neuronal damage without suppressing fungal clearance. CD4+ T cell accumulation and TH1 skewing are reduced in the CNS but not spleens of infected CXCR3-/- mice. Adoptive transfer of WT, but not CXCR3-/- CD4+ T cells, into CXCR3-/- mice phenocopies the pathology of infected WT mice. Collectively, we found that CXCR3+CD4+ T cells drive lethal CNS pathology but are not required for fungal clearance during CM. The CXCR3 pathway shows potential as a therapeutic target or for biomarker discovery to limit CNS inflammatory damages.

In Vitro Immunological Effects of CXCR3 Inhibitor AMG487 on Dendritic Cells

AMG 487 is the targeted blocker of chemokine receptor CXCR3 and improves inflammatory symptoms by blocking the inflammatory cycle. Here we investigated whether AMG 487 affects dendritic cell (DC) biology and function. The expression of co-stimulatory markers on DCs was reduced, indicating the semi-mature state of DC when AMG 487 was added throughout the in vitro differentiation period. Additionally, when added solely during the final lipopolysaccharide-induced activation step, AMG 487 inhibited DC activation, as demonstrated by a decreased expression of activation markers. AMG487 also promoted the expression of PD-L2 and impaired the ability to induce antigen-specific T cell responses. Our results demonstrated that AMG 487 significantly affects DC maturity in vitro and function leading to impaired T cell activation, inducing DCs to have characteristics similar to tolerogenic DCs. AMG 487 may directly play an immunomodulatory role during DC development and functional shaping.

Insight into structural requirements for selective and/or dual CXCR3 and CXCR4 allosteric modulators

Based on the previously published pyrazolopyridine-based hit compound for which negative allosteric modulation of both CXCR3 and CXCR4 receptors was disclosed, we designed, synthesized and biologically evaluated a set of novel, not only negative, but also positive allosteric modulators with preserved pyrazolopyridine core. Compound 9e is a dual negative modulator, inhibiting G protein activity of both receptors. For CXCR4 receptor para-substituted aromatic group of compounds distinguishes between negative and positive modulation. Para-methoxy substitution leads to functional antagonism, while para-chloro triggers agonism. Additionally, we discovered that chemotaxis is not completely correlated with G protein pathways. This is the first work in which we have on a series of compounds successfully demonstrated that it is possible to produce selective as well as dual-acting modulators of chemokine receptors, which is very promising for future research in the field of discovery of selective or dual modulators of chemokine receptors.

Differential role of CXCR3 in inflammation and colorectal cancer

Chemokines (CXCR3) and their ligands (CXCL9, CXCL10, and CXCL11) exert exquisite control over T-cell trafficking and are critical for activation, differentiation and effector T cell function. CXCR3 is important for CD4 Th1 cells, CD8 effectors, memory cells, and for the function of natural killer and natural killer T cells. The presence of high cytotoxic CXCR3 ligand expression on CD8 T cells in colorectal cancerous tissue has been well documented in the past. CXCR3 and its ligands are differentially expressed at sites of inflammation and within the tumors. Further, the expression of CXCR3 and its ligands has been correlated with both the presence of effector T cells within tumor tissue and disease-free survival of patients. However, effector T cell infiltration into primary and metastatic tumors is highly variable and, in fact, often absent. Thus, understanding why T cells fail to infiltrate into tumors and determining the way to improve effector T cell entry into tumors would be important advances in efforts to harness the power of the immune system to fight cancer. To this end, the recent exciting discovery that CXCR3 is functionally expressed on regulatory T cells and also induces the differentiation of peripheral CD4 T cells into regulatory T cells, might address the novel clinically relevant question of the therapeutic potential of the CXCR3 system. This is also coupled with the fact that increases in CXCR3 expression also improves effector T cell function. This review describes the differential role of CXCR3 induction on peripheral and tumor microenvironment inflammation. Further, this review, tied with important findings from our laboratory, demonstrates that polyphenols induce CXCR3 expression on regulatory T cells and increases CXCR3 ligands in the tumor microenvironment, which act together to suppress colorectal cancer through a differential mechanism discussed herewith.

Molecular Mechanisms of Biased and Probe-Dependent Signaling at CXC-Motif Chemokine Receptor CXCR3 Induced by Negative Allosteric Modulators

Our recent explorations of allosteric modulators with improved properties resulted in the identification of two biased negative allosteric modulators, BD103 (N-1-{[3-(4-ethoxyphenyl)-4-oxo-3,4-dihydropyrido[2,3-d]pyrimi-din2yl]ethyl}-4-(4-fluorobutoxy)-N-[(1-methylpiperidin-4-yl)methyl}]butanamide) and BD064 (5-[(N-{1-[3-(4-ethoxyphenyl)-4-oxo-3,4-dihydropyrido[2,3-d]pyrimidin-2-yl]ethyl-2-[4-fluoro-3-(trifluoromethyl)phenyl]acetamido)methyl]-2-fluorophenyl}boronic acid), that exhibited probe-dependent inhibition of CXC-motif chemokine receptor CXCR3 signaling. With the intention to elucidate the structural mechanisms underlying their selectivity and probe dependence, we used site-directed mutagenesis combined with homology modeling and docking to identify amino acids of CXCR3 that contribute to modulator binding, signaling, and transmission of cooperativity. With the use of allosteric radioligand RAMX3 ([3H]N-{1-[3-(4-ethoxyphenyl)-4-oxo-3,4-dihydropyrido[2,3-d]pyrimidin-2-yl]ethyl}-2-[4-fluoro-3-(trifluoromethyl)phenyl]-N-[(1-methylpiperidin-4-yl)methyl]acetamide), we identified that F1313.32 and Y3087.43 contribute specifically to the binding pocket of BD064, whereas D1864.60 solely participates in the stabilization of binding conformation of BD103. The influence of mutations on the ability of negative allosteric modulators to inhibit chemokine-mediated activation (CXCL11 and CXCL10) was assessed with the bioluminescence resonance energy transfer-based cAMP and β-arrestin recruitment assay. Obtained data revealed complex molecular mechanisms governing biased and probe-dependent signaling at CXCR3. In particular, F1313.32, S3047.39, and Y3087.43 emerged as key residues for the compounds to modulate the chemokine response. Notably, D1864.60, W2686.48, and S3047.39 turned out to play a role in signal pathway selectivity of CXCL10, as mutations of these residues led to a G protein-active but β-arrestin-inactive conformation. These diverse effects of mutations suggest the existence of ligand- and pathway-specific receptor conformations and give new insights in the sophisticated signaling machinery between allosteric ligands, chemokines, and their receptors, which can provide a powerful platform for the development of new allosteric drugs with improved pharmacological properties.

Critical Role of the CXCL10/C-X-C Chemokine Receptor 3 Axis in Promoting Leukocyte Recruitment and Neuronal Injury during Traumatic Optic Neuropathy Induced by Optic Nerve Crush

Traumatic optic neuropathy (TON) is an acute injury of the optic nerve secondary to trauma. Loss of retinal ganglion cells (RGCs) is a key pathological process in TON, yet mechanisms responsible for RGC death remain unclear. In a mouse model of TON, real-time noninvasive imaging revealed a dramatic increase in leukocyte rolling and adhesion in veins near the optic nerve (ON) head at 9 hours after ON injury. Although RGC dysfunction and loss were not detected at 24 hours after injury, massive leukocyte infiltration was observed in the superficial retina. These cells were identified as T cells, microglia/monocytes, and neutrophils but not B cells. CXCL10 is a chemokine that recruits leukocytes after binding to its receptor C-X-C chemokine receptor (CXCR) 3. The levels of CXCL10 and CXCR3 were markedly elevated in TON, and up-regulation of CXCL10 was mediated by STAT1/3. Deleting CXCR3 in leukocytes significantly reduced leukocyte recruitment, and prevented RGC death at 7 days after ON injury. Treatment with CXCR3 antagonist attenuated TON-induced RGC dysfunction and cell loss. In vitro co-culture of primary RGCs with leukocytes resulted in increased RGC apoptosis, which was exaggerated in the presence of CXCL10. These results indicate that leukocyte recruitment in retinal vessels near the ON head is an early event in TON and the CXCL10/CXCR3 axis has a critical role in recruiting leukocytes and inducing RGC death.

Pediatric Kawasaki Disease and Adult Human Immunodeficiency Virus Kawasaki-Like Syndrome Are Likely the Same Malady

Background.  Pediatric Kawasaki disease (KD) and human immunodeficiency virus (HIV)⁺ adult Kawasaki-like syndrome (KLS) are dramatic vasculitides with similar physical findings. Both syndromes include unusual arterial histopathology with immunoglobulin (Ig)A⁺ plasma cells, and both impressively respond to pooled Ig therapy. Their distinctive presentations, histopathology, and therapeutic response suggest a common etiology. Because blood is in immediate contact with inflamed arteries, we investigated whether KD and KLS share an inflammatory signature in serum. Methods.  A custom multiplex enzyme-linked immunosorbent assay (ELISA) defined the serum cytokine milieu in 2 adults with KLS during acute and convalescent phases, with asymptomatic HIV⁺ subjects not taking antiretroviral therapy serving as controls. We then prospectively collected serum and plasma samples from children hospitalized with KD, unrelated febrile illnesses, and noninfectious conditions, analyzing them with a custom multiplex ELISA based on the KLS data. Results.  Patients with KLS and KD subjects shared an inflammatory signature including acute-phase reactants reflecting tumor necrosis factor (TNF)-α biologic activity (soluble TNF receptor I/II) and endothelial/smooth muscle chemokines Ccl1 (Th2), Ccl2 (vascular inflammation), and Cxcl11 (plasma cell recruitment). Ccl1 was specifically elevated in KD versus febrile controls, suggesting a unique relationship between Ccl1 and KD/KLS pathogenesis. Conclusions.  This study defines a KD/KLS inflammatory signature mirroring a dysfunctional response likely to a common etiologic agent. The KD/KLS inflammatory signature based on elevated acute-phase reactants and specific endothelial/smooth muscle chemokines was able to identify KD subjects versus febrile controls, and it may serve as a practicable diagnostic test for KD.

Small Molecule CXCR3 Antagonists

Chemokines and their receptors are known to play important roles in disease. More than 40 chemokine ligands and 20 chemokine receptors have been identified, but, to date, only two small molecule chemokine receptor antagonists have been approved by the FDA. The chemokine receptor CXCR3 was identified in 1996, and nearly 20 years later, new areas of CXCR3 disease biology continue to emerge. Several classes of small molecule CXCR3 antagonists have been developed, and two have shown efficacy in preclinical models of inflammatory disease. However, only one CXCR3 antagonist has been evaluated in clinical trials, and there remain many opportunities to further investigate known classes of CXCR3 antagonists and to identify new chemotypes. This Perspective reviews the known CXCR3 antagonists and considers future opportunities for the development of small molecules for clinical evaluation.

Metabolic profiling of ligands for the chemokine receptor CXCR3 by liquid chromatography-mass spectrometry coupled to bioaffinity assessment

Chemokine receptors belong to the class of G protein-coupled receptors and are important in the host defense against infections and inflammation. However, aberrant chemokine signaling is linked to different disorders such as cancer, central nervous system and immune disorders, and viral infections [Scholten DJ et al. (2012) Br J Pharmacol 165(6):1617–1643]. Modulating the chemokine receptor function provides new ways of targeting specific diseases. Therefore, discovery and development of drugs targeting chemokine receptors have received considerable attention from the pharmaceutical industry in the past decade. Along with that, the determination of bioactivities of individual metabolites derived from lead compounds towards chemokine receptors is crucial for drug selectivity, pharmacodynamics, and potential toxicity issues. Therefore, advanced analytical methodologies are in high demand. This study is aimed at the optimization of a new analytical method for metabolic profiling with parallel bioaffinity assessment of CXCR3 ligands of the azaquinazolinone and piperazinyl-piperidine class and their metabolites. The method is based on mass spectrometric (MS) identification after liquid chromatographic (LC) separation of metabolic mixtures. The bioaffinity assessment is performed “at-line” via high-resolution nanofractionation onto 96-well plates allowing direct integration of radioligand binding assays. This new method enables identification of metabolites from lead compounds with associated estimation of their individual bioaffinity. Moreover, the identification of the metabolite structures via accurate mass measurements and MS² allows the identification of liable metabolic “hotspots” for further lead optimization. The efficient combination of chemokine receptor ligand binding assays with analytical techniques, involving nanofractionation as linking technology, allows implementation of comprehensive metabolic profiling in an early phase of the drug discovery process.

Pharmacological characterization of [3H]VUF11211, a novel radiolabeled small-molecule inverse agonist for the chemokine receptor CXCR3

Chemokine receptor CXCR3 has attracted much attention, as it is thought to be associated with a wide range of immune-related diseases. As such, several small molecules with different chemical structures targeting CXCR3 have been discovered. Despite limited clinical success so far, these compounds serve as interesting tools for investigating receptor activation and antagonism. Accumulating evidence suggests that many of these compounds are allosteric modulators for CXCR3. One feature of allosteric ligands is that the magnitude of the mediated allosteric effect is dependent on the orthosteric probe that is used. Consequently, there is a risk for incorrect assessment of affinity for allosteric modulators with orthosteric radioligands, which has so far been the most applied approach for chemokine receptors. Therefore, we aimed to use a small-molecule allosteric ligand from the piperazinyl-piperidine class, also known as VUF11211 [(S)-5-chloro-6-(4-(1-(4-chlorobenzyl)piperidin-4-yl)-3-ethylpiperazin-1-yl)-N-ethylnicotinamide]. VUF11211 acts as an inverse agonist at a constitutively active mutant of CXCR3. Radiolabeling of VUF11211 gave [(3)H]VUF11211, which in radioligand binding studies shows high affinity for CXCR3 (Kd = 0.65 nM) and reasonably fast association (kon= 0.03 minute(-1)nM(-1)) and dissociation kinetics (koff = 0.02 minute(-1)). The application of the [(3)H]VUF11211 to assess CXCR3 pharmacology was validated with diverse classes of CXCR3 compounds, including both antagonists and agonists, as well as VUF11211 analogs. Interestingly, VUF11211 seems to bind to a different population of CXCR3 conformations compared with the CXCR3 agonists CXC chemokine ligand 11 (CXCL11), VUF11418 [1-((1R,5S)-6,6-dimethylbicyclo[3.1.1]hept-2-en-2-yl)-N-((2'-iodobiphenyl-4-yl)methyl)-N,N-dimethylmethanaminium Iodide], and VUF10661 [N-(6-amino-1-(2,2-diphenylethylamino)-1-oxohexan-2-yl)-2-(4-oxo-4-phenylbutanoyl)-1,2,3,4-tetrahydroisoquinoline-3-carboxamide]. These findings, taken together, indicate that this allosteric inverse agonist radioligand for CXCR3 may facilitate the discovery, characterization, and optimization of allosteric modulators for the chemokine receptor CXCR3.

CXCL10 is critical for the progression and maintenance of depigmentation in a mouse model of vitiligo

Vitiligo is an autoimmune disease of the skin that results in disfiguring white spots. There are no U.S. Food and Drug Administration-approved treatments for vitiligo, and most off-label treatments yield unsatisfactory results. Vitiligo patients have increased numbers of autoreactive, melanocyte-specific CD8(+) T cells in the skin and blood, which are directly responsible for melanocyte destruction. We report that gene expression in lesional skin from vitiligo patients revealed an interferon-γ (IFN-γ)-specific signature, including the chemokine CXCL10. CXCL10 was elevated in both vitiligo patient skin and serum, and CXCR3, its receptor, was expressed on pathogenic T cells. To address the function of CXCL10 in vitiligo, we used a mouse model of disease that also exhibited an IFN-γ-specific gene signature, expression of CXCL10 in the skin, and up-regulation of CXCR3 on antigen-specific T cells. Mice that received Cxcr3(-/-) T cells developed minimal depigmentation, as did mice lacking Cxcl10 or treated with CXCL10-neutralizing antibody. CXCL9 promoted autoreactive T cell global recruitment to the skin but not effector function, whereas CXCL10 was required for effector function and localization within the skin. Surprisingly, CXCL10 neutralization in mice with established, widespread depigmentation induces reversal of disease, evidenced by repigmentation. These data identify a critical role for CXCL10 in both the progression and maintenance of vitiligo and thereby support inhibiting CXCL10 as a targeted treatment strategy.

Boronic acids as probes for investigation of allosteric modulation of the chemokine receptor CXCR3

The chemokine receptor CXCR3 is a G protein-coupled receptor, which conveys extracellular signals into cells by changing its conformation upon agonist binding. To facilitate the mechanistic understanding of allosteric modulation of CXCR3, we combined computational modeling with the synthesis of novel chemical tools containing boronic acid moiety, site-directed mutagenesis, and detailed functional characterization. The design of boronic acid derivatives was based on the predictions from homology modeling and docking. The choice of the boronic acid moiety was dictated by its unique ability to interact with proteins in a reversible covalent way, thereby influencing conformational dynamics of target biomolecules. During the synthesis of the library we have developed a novel approach for the purification of drug-like boronic acids. To validate the predicted binding mode and to identify amino acid residues responsible for the transduction of signal through CXCR3, we conducted a site-directed mutagenesis study. With the use of allosteric radioligand RAMX3 we were able to establish the existence of a second allosteric binding pocket in CXCR3, which enables different binding modes of structurally closely related allosteric modulators of CXCR3. We have also identified residues Trp109(2.60) and Lys300(7.35) inside the transmembrane bundle of the receptor as crucial for the regulation of the G protein activation. Furthermore, we report the boronic acid 14 as the first biased negative allosteric modulator of the receptor. Overall, our data demonstrate that boronic acid derivatives represent an outstanding tool for determination of key receptor-ligand interactions and induction of ligand-biased signaling.

Biased and g protein-independent signaling of chemokine receptors

Biased signaling or functional selectivity occurs when a 7TM-receptor preferentially activates one of several available pathways. It can be divided into three distinct forms: ligand bias, receptor bias, and tissue or cell bias, where it is mediated by different ligands (on the same receptor), different receptors (with the same ligand), or different tissues or cells (for the same ligand–receptor pair). Most often biased signaling is differentiated into G protein-dependent and β-arrestin-dependent signaling. Yet, it may also cover signaling differences within these groups. Moreover, it may not be absolute, i.e., full versus no activation. Here we discuss biased signaling in the chemokine system, including the structural basis for biased signaling in chemokine receptors, as well as in class A 7TM receptors in general. This includes overall helical movements and the contributions of micro-switches based on recently published 7TM crystals and molecular dynamics studies. All three forms of biased signaling are abundant in the chemokine system. This challenges our understanding of “classic” redundancy inevitably ascribed to this system, where multiple chemokines bind to the same receptor and where a single chemokine may bind to several receptors – in both cases with the same functional outcome. The ubiquitous biased signaling confers a hitherto unknown specificity to the chemokine system with a complex interaction pattern that is better described as promiscuous with context-defined roles and different functional outcomes in a ligand-, receptor-, or cell/tissue-defined manner. As the low number of successful drug development plans implies, there are great difficulties in targeting chemokine receptors; in particular with regard to receptor antagonists as anti-inflammatory drugs. Un-defined and putative non-selective targeting of the complete cellular signaling system could be the underlying cause of lack of success. Therefore, biased ligands could be the solution.

IV. Discovery of CXCR3 antagonists substituted with heterocycles as amide surrogates: improved PK, hERG and metabolic profiles

The structure-human CXCR3 binding affinity relationship of a series of pyridyl/pyrazinyl-piperazinyl-piperidine derivatives were explored with a focus to improve PK, hERG and metabolic profiles. Several small heterocycles were identified as amide surrogates, which minimized many potential metabolite issues. During the course of SAR development, we have observed the additive effect of desirable functional groups to improve hERG and PK profiles which lead to the discovery of many clinically developable CXCR3 antagonists with excellent overall profile.

Identification of overlapping but differential binding sites for the high-affinity CXCR3 antagonists NBI-74330 and VUF11211

CXC chemokine receptor CXCR3 and/or its main three ligands CXCL9, CXCL10, and CXCL11 are highly upregulated in a variety of diseases. As such, considerable efforts have been made to develop small-molecule receptor CXCR3 antagonists, yielding distinct chemical classes of antagonists blocking binding and/or function of CXCR3 chemokines. Although it is suggested that these compounds bind in an allosteric fashion, thus far no evidence has been provided regarding the molecular details of their interaction with CXCR3. Using site-directed mutagenesis complemented with in silico homology modeling, we report the binding modes of two high-affinity CXCR3 antagonists of distinct chemotypes: VUF11211 [(S)-5-chloro-6-(4-(1-(4-chlorobenzyl)piperidin-4-yl)-3-ethylpiperazin-1-yl)-N-ethylnicotinamide] (piperazinyl-piperidine) with a rigid elongated structure containing two basic groups and NBI-74330 [(R)-N-(1-(3-(4-ethoxyphenyl)-4-oxo-3,4-dihydropyrido[2,3-d]pyrimidin-2-yl)ethyl)-2-(4-fluoro-3-(trifluoromethyl)phenyl)-N-(pyridin-3-ylmethyl)acetamide] (8-azaquinazolinone) without any basic group. Here we show that NBI-74330 is anchored in the transmembrane minor pocket lined by helices 2 (W2.60, D2.63), 3 (F3.32), and 7 (S7.39, Y7.43), whereas VUF11211 extends from the minor pocket into the major pocket of the transmembrane domains, located between residues in helices 1 (Y1.39), 2 (W2.60), 3 (F3.32), 4 (D4.60), 6 (Y6.51), and 7 (S7.39, Y7.43). Mutation of these residues did not affect CXCL11 binding significantly, confirming the allosteric nature of the interaction of these small molecules with CXCR3. Moreover, the model derived from our in silico-guided studies fits well with the already published structure-activity relationship data on these ligands. Altogether, in this study, we show overlapping, yet different binding sites for two high-affinity CXCR3 antagonists, which offer new opportunities for the structure-based design of allosteric modulators for CXCR3.

Identification and profiling of CXCR3-CXCR4 chemokine receptor heteromer complexes

BACKGROUND AND PURPOSE

The C-X-C chemokine receptors 3 (CXCR3) and C-X-C chemokine receptors 4 (CXCR4) are involved in various autoimmune diseases and cancers. Small antagonists have previously been shown to cross-inhibit chemokine binding to CXCR4, CC chemokine receptors 2 (CCR2) and 5 (CCR5) heteromers. We investigated whether CXCR3 and CXCR4 can form heteromeric complexes and the binding characteristics of chemokines and small ligand compounds to these chemokine receptor heteromers.

EXPERIMENTAL APPROACH

CXCR3-CXCR4 heteromers were identified in HEK293T cells using co-immunoprecipitation, time-resolved fluorescence resonance energy transfer, saturation BRET and the GPCR-heteromer identification technology (HIT) approach. Equilibrium competition binding and dissociation experiments were performed to detect negative binding cooperativity.

KEY RESULTS

We provide evidence that chemokine receptors CXCR3 and CXCR4 form heteromeric complexes in HEK293T cells. Chemokine binding was mutually exclusive on membranes co-expressing CXCR3 and CXCR4 as revealed by equilibrium competition binding and dissociation experiments. The small CXCR3 agonist VUF10661 impaired binding of CXCL12 to CXCR4, whereas small antagonists were unable to cross-inhibit chemokine binding to the other chemokine receptor. In contrast, negative binding cooperativity between CXCR3 and CXCR4 chemokines was not observed in intact cells. However, using the GPCR-HIT approach, we have evidence for specific β-arrestin2 recruitment to CXCR3-CXCR4 heteromers in response to agonist stimulation.

CONCLUSIONS AND IMPLICATIONS

This study indicates that heteromeric CXCR3-CXCR4 complexes may act as functional units in living cells, which potentially open up novel therapeutic opportunities.

Photodynamic agents with anti-metastatic activities

A new concept in multifunctional anticancer agents is demonstrated. Tetrakis-(diisopropyl-guanidino) zinc phthalocyanine (Zn-DIGP) exhibits excellent properties as a photodynamic therapy (PDT) agent, as well as potential anti-metastatic activities in vivo. Zn-DIGP exhibits good cellular uptake and low toxicity in the dark (EC50 > 80 μM) and is well tolerated upon its intravenous injection into mice at 8 mg/kg. Upon photoexcitation with red laser light (660 nm), Zn-DIGP exhibits a high quantum yield for singlet oxygen formation (Φ ≈ 0.51) that results in potent phototoxicity to cell cultures (EC50 ≈ 0.16 μM). Zn-DIGP is also capable of inhibiting the formation of tumor colonies in the lungs of C57BL/6 mice injected with B16F10 cells. Zn-DIGP therefore inhibits cancer growth by both light-dependent and light-independent pathways. The anti-metastatic activities of Zn-DIGP possibly result from its ability to interfere with the signaling between chemokine CXCL10 and the G protein-coupled receptor CXCR3. Zn-DIGP is a competitive inhibitor of CXCR3 activation (IC50 = 3.8 μM) and selectively inhibits downstream events such as CXCL10-activated cell migration. Consistent with the presence of feedback regulation between CXCR3 binding and CXCL10 expression, Zn-DIGP causes overexpression of CXCL10. Interestingly, Zn-DIGP binds to CXCR3 without activating the receptor yet is able to cause endocytosis and degradation of this GPCR. To the best of our knowledge, Zn-DIGP is the first PDT agent that can facilitate the photodynamic treatment of primary tumors while simultaneously inhibiting the formation of metastatic tumor colonies by a light-independent mode of action.

Dichotomy of CCL21 and CXCR3 in nerve injury-evoked and autoimmunity-evoked hyperalgesia

The chemokine CCL21 is released from injured neurons and acts as a ligand of the chemokine receptor, CXCR3, which likely contributes to pro-inflammatory adaptations and secondary neuronal damage. CCL21-CXCR3 signalling may therefore impact on the development of neuropathic pain. By using the respective knockout mice we show that deficiency of CCL19/21 in plt/plt mice attenuates nerve injury evoked pain but not the hyperalgesia evoked by autoimmune encephalomyelitis (EAE). Oppositely, CXCR3-deficiency had no protective effect after traumatic nerve injury but reduced EAE-evoked hyperalgesia and was associated with reduced clinical EAE scores, a reduction of the pro-inflammatory cell infiltration and reduced upregulation of interferon gamma and interleukin-17 in the spinal cord. In contrast, microglia activation in the spinal cord after traumatic sciatic nerve injury was neither attenuated in CXCR3(-/-) nor plt/plt mice, nor in double knockouts. However, the severity of EAE, but not the hyperalgesia, was also reduced in plt/plt mice, which was associated with reduced infiltration of the spinal cord with CCR7+ T-cells, an increase of CD25+ T-cells and reduced upregulation of CXCL9 and 10, CCL11 and 12. The data show that CCL21 and CXCR3 have dichotomous functions in traumatic and EAE-evoked neuropathic pain suggesting diverse mechanisms likely requiring diverse treatments although both types of neuropathic pain are mediated in part through the immune activation.

The Novartis view on emerging drugs and novel targets for the treatment of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a debilitating lung disease characterized by airflow limitation and chronic inflammation in the lungs. The mainstay of drug therapy for COPD is represented by long-acting bronchodilators, an important aspect of Novartis' development program. Novel once-daily dosing bronchodilators, such as the long-acting muscarinic antagonist (LAMA) glycopyrronium and the LAMA/long-acting β2-agonist (LABA) fixed-dose combination QVA149, have been shown to provide significant benefits to patients with COPD in terms of improvement in lung function, exercise tolerance, health-related quality of life, symptoms and reduction in the rate of exacerbations. Despite the benefits provided by these new treatment options, prevention of disease progression and control of exacerbations in certain patient phenotypes remain key challenges in the treatment of COPD. In order to address these needs and gain new insights into the complexity of COPD, Novartis is, in addition to bronchodilator-only therapies, developing LABA/inhaled corticosteroids (ICS) combinations to target inflammation, such as QMF149, as well as non-steroid based anti-inflammatory agents against key novel targets. These commitments are central to the Novartis' final goal of improving the standard of care in respiratory medicine and offering a better quality of life to patients with COPD.

Early differentiated CD138(high) MHCII+ IgG+ plasma cells express CXCR3 and localize into inflamed kidneys of lupus mice

Humoral responses are central to the development of chronic autoimmune diseases such as systemic lupus erythematosus. Indeed, autoantibody deposition is responsible for tissue damage, the kidneys being one of the main target organs. As the source of pathogenic antibodies, plasma cells are therefore critical players in this harmful scenario, both at systemic and local levels. The aim of the present study was to analyze plasma cells in NZB/W lupus mice and to get a better understanding of the mechanisms underlying their involvement in the renal inflammation process. Using various techniques (i.e. flow cytometry, quantitative PCR, ELISpot), we identified and extensively characterized three plasma cell intermediates, according to their B220/CD138/MHCII expression levels. Each of these cell subsets displays specific proliferation and antibody secretion capacities. Moreover, we evidenced that the inflammation-related CXCR3 chemokine receptor is uniquely expressed by CD138^highMHCII⁺ plasma cells, which encompass both short- and long-lived cells and mostly produce IgG (auto)antibodies. Expression of CXCR3 allows efficient chemotactic responsiveness of these cells to cognate chemokines, which production is up-regulated in the kidneys of diseased NZB/W mice. Finally, using fluorescence and electron microscopy, we demonstrated the presence of CD138⁺CXCR3⁺IgG⁺ cells in inflammatory areas in the kidneys, where they are very likely involved in the injury process. Thus, early differentiated CD138^highMHCII⁺ rather than terminally differentiated CD138^highMHCII^low plasma cells may be involved in the renal inflammatory injury in lupus, due to CXCR3 expression and IgG secretion.

Pharmacological characterization of a small-molecule agonist for the chemokine receptor CXCR3

BACKGROUND AND PURPOSE

The chemokine receptor CXCR3 is a GPCR found predominantly on activated T cells. CXCR3 is activated by three endogenous peptides; CXCL9, CXCL10 and CXCL11. Recently, a small-molecule agonist, VUF10661, has been reported in the literature and synthesized in our laboratory. The aim of the present study was to provide a detailed pharmacological characterization of VUF10661 by comparing its effects with those of CXCL11.

EXPERIMENTAL APPROACH

Agonistic properties of VUF10661 were assessed in a chemotaxis assay with murine L1.2 cells transiently transfected with cDNA encoding the human CXCR3 receptor and in binding studies, with [(125)I]-CXCL10 and [(125)I]-CXCL11, on membrane preparations from HEK293 cells stably expressing CXCR3. [(35)S]-GTPγS binding was used to determine its potency to induce CXCR3-mediated G protein activation and BRET-based assays to investigate its effects on intracellular cAMP levels and β-arrestin recruitment.

KEY RESULTS

VUF10661 acted as a partial agonist in CXCR3-mediated chemotaxis, bound to CXCR3 in an allosteric fashion in ligand binding assays and activated G(i) proteins with the same efficacy as CXCL11 in the [(35)S]-GTPγS binding and cAMP assay, while it recruited more β-arrestin1 and β-arrestin2 to CXCR3 receptors than the chemokine.

CONCLUSIONS AND IMPLICATIONS

VUF10661, like CXCL11, activates both G protein-dependent and -independent signalling via the CXCR3 receptor, but probably exerts its effects from an allosteric binding site that is different from that for CXCL11. It could stabilize different receptor and/or β-arrestin conformations leading to differences in functional output. Such ligand-biased signalling might offer interesting options for the therapeutic use of CXCR3 agonists.

Therapeutic efficacy of CXCR3 blockade in an experimental model of severe sepsis

Introduction

In our previous studies we demonstrated that CXC chemokine receptor 3 (CXCR3) participates in the regulation of lymphocyte trafficking during cecal ligation and puncture (CLP)-induced sepsis. In this study, we evaluated the effects of treatment with anti-CXCR3 immunoglobulin (IgG) and antibiotics on outcome during septic shock caused by CLP.

Methods

C57BL/6J mice were treated with neutralizing IgG against CXCR3 plus Primaxin either 24 hours prior to, 2 hours after or 6 hours after CLP. Control mice received nonspecific IgG plus Primaxin in the same regimen. Survival, core body temperature, bacterial clearance and systemic cytokine production were evaluated.

Results

Our results show that treatment with anti-CXCR3 IgG plus Primaxin significantly improved survival when administered 24 hours prior to CLP (50% vs. 10%), 2 hours after CLP (55% vs. 10%) or 6 hours after CLP (55% vs. 25%) compared with mice receiving nonspecific IgG plus Primaxin. Treatment with anti-CXCR3 plus Primaxin 24 hours prior to CLP attenuated hypothermia and IL-6 and macrophage inflammatory protein 2 (MIP-2) production but did not alter bacterial clearance. Treatment with anti-CXCR3 IgG and Primaxin 2 hours after CLP did not improve bacterial clearance and systemic cytokine production compared with mice treated with IgG and Primaxin, whereas 6 hours after CLP the bacterial clearance and IL-6 and MIP-2 concentrations, both in plasma and peritoneal lavage fluid, were significantly improved in mice receiving anti-CXCR3 IgG and Primaxin compared with mice that only received nonspecific IgG and Primaxin.

Conclusion

The results from this study indicate that neutralization of CXCR3 prior to, 2 hours after or 6 hours after the initiation of CLP-induced septic shock improves survival and attenuates CLP-induced inflammation and physiologic dysfunction.

The emerging role of CXC chemokines and their receptors in cancer

Chemokines and their receptors have a multifaceted role in tumor biology and are implicated in nearly all aspects of cancer growth, survival and dissemination. Modulation of the interaction between chemokines and their cell surface receptor is, therefore, a promising area for the development of new cancer medicines. In this review, we look at the compelling evidence that is emerging to support targeting CXC chemokines, also known as family α chemokines, as novel therapeutic strategies in the treatment of cancer.

HIV persistence: chemokines and their signalling pathways

Latently infected resting CD4+ T cells are the major barrier to curing HIV. We have recently demonstrated that chemokines, which bind to the chemokine receptors CCR7, CXCR3 and CCR6, facilitate efficient HIV nuclear localisation and integration in resting CD4+ T cells, leading to latency. As latently infected cells are enriched in lymphoid tissues, where chemokines are highly concentrated, this may provide a mechanism for the generation of latently infected cells in vivo. Here we review the role of chemokines in HIV persistence; the main signalling pathways that are involved; and how these pathways may be exploited to develop novel strategies to reduce or eliminate latently infected cells.

Differential Expression of Chemokine Receptors and their Roles in Cancer Imaging

Chemokine/chemokine receptor interactions play diverse roles in cell migration and homeostasis. Emerging evidence suggests that cancer cells co-opt chemokine networks for survival, proliferation, immune evasion, and metastasis. Most of the chemokine receptors are reported to be involved in tumor progression. Given their extensive implication in cancer progression, several chemokine receptor/ligand axes are considered as potential therapeutic targets. This review provides a survey of chemokine receptor expression in cancer and evaluates the potential of chemokine receptor imaging as a tool for molecular characterization of cancer.

Chemokine-dependent B cell-T cell interactions in chronic lymphocytic leukemia and multiple myeloma - targets for therapeutic intervention?

INTRODUCTION

Chemokines and their receptors play essential roles in the development, maintenance and proper functioning of the immune system. B cell-T cell interactions are modulated by chemokines. In B cell malignancies, these interactions may have tumor-promoting consequences.

AREAS COVERED

This review summarizes physiological B cell-T cell interactions and discusses their pathological role in the onset and progression of B cell malignancies with a special focus on chronic lymphocytic leukemia and multiple myeloma. Experimental data on chemokine-guided B cell-T cell actions in B cell malignancies from murine models as well as in vitro data are summarized and their potential as future therapeutic targets is critically discussed.

EXPERT OPINION

Direct or indirect targeting of chemokine receptors involved in localization and T-cell-dependent activation of B lymphocytes can provide strong synergisms with conventional or immunomodulatory therapies by disrupting the microenvironmental conditions necessary for survival and proliferation of malignant B lymphocytes. However, further knowledge of these interactions between B and T cells is needed.

A selective and potent CXCR3 antagonist SCH 546738 attenuates the development of autoimmune diseases and delays graft rejection

BACKGROUND

The CXCR3 receptor and its three interferon-inducible ligands (CXCL9, CXCL10 and CXCL11) have been implicated as playing a central role in directing a Th1 inflammatory response. Recent studies strongly support that the CXCR3 receptor is a very attractive therapeutic target for treating autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis and psoriasis, and to prevent transplant rejection. We describe here the in vitro and in vivo pharmacological characterizations of a novel and potent small molecule CXCR3 antagonist, SCH 546738.

RESULTS

In this study, we evaluated in vitro pharmacological properties of SCH 546738 by radioligand receptor binding and human activated T cell chemotaxis assays. In vivo efficacy of SCH 546738 was determined by mouse collagen-induced arthritis, rat and mouse experimental autoimmune encephalomyelitis, and rat cardiac transplantation models. We show that SCH 546738 binds to human CXCR3 with a high affinity of 0.4 nM. In addition, SCH 546738 displaces radiolabeled CXCL10 and CXCL11 from human CXCR3 with IC50 ranging from 0.8 to 2.2 nM in a non-competitive manner. SCH 546738 potently and specifically inhibits CXCR3-mediated chemotaxis in human activated T cells with IC90 about 10 nM. SCH 546738 attenuates the disease development in mouse collagen-induced arthritis model. SCH 546738 also significantly reduces disease severity in rat and mouse experimental autoimmune encephalomyelitis models. Furthermore, SCH 546738 alone achieves dose-dependent prolongation of rat cardiac allograft survival. Most significantly, SCH 546738 in combination with CsA supports permanent engraftment.

CONCLUSIONS

SCH 546738 is a novel, potent and non-competitive small molecule CXCR3 antagonist. It is efficacious in multiple preclinical disease models. These results demonstrate that therapy with CXCR3 antagonists may serve as a new strategy for treatment of autoimmune diseases, including rheumatoid arthritis and multiple sclerosis, and to prevent transplant rejection.

A chemokine gene expression signature derived from meta-analysis predicts the pathogenicity of viral respiratory infections

BACKGROUND

During respiratory viral infections host injury occurs due in part to inappropriate host responses. In this study we sought to uncover the host transcriptional responses underlying differences between high- and low-pathogenic infections.

RESULTS

From a compendium of 12 studies that included responses to influenza A subtype H5N1, reconstructed 1918 influenza A virus, and SARS coronavirus, we used meta-analysis to derive multiple gene expression signatures. We compared these signatures by their capacity to segregate biological conditions by pathogenicity and predict pathogenicity in a test data set. The highest-performing signature was expressed as a continuum in low-, medium-, and high-pathogenicity samples, suggesting a direct, analog relationship between expression and pathogenicity. This signature comprised 57 genes including a subnetwork of chemokines, implicating dysregulated cell recruitment in injury.

CONCLUSIONS

Highly pathogenic viruses elicit expression of many of the same key genes as lower pathogenic viruses but to a higher degree. This increased degree of expression may result in the uncontrolled co-localization of inflammatory cell types and lead to irreversible host damage.

Molecular mechanisms of liver metastasis

Colorectal cancer is the second most common cancer, and is the third leading cause of cancer-related death in Japan. The majority of these deaths is attributable to liver metastasis. Recent studies have provided increasing evidence that the chemokine-chemokine receptor system is a potential mechanism of tumor metastasis via multiple complementary actions: (a) by promoting cancer cell migration, invasion, survival and angiogenesis; and (b) by recruiting distal stromal cells (i.e., myeloid bone marrow-derived cells) to indirectly facilitate tumor invasion and metastasis. Here, we discuss recent preclinical and clinical data supporting the view that chemokine pathways are potential therapeutic targets for liver metastasis of colorectal cancer.